The daft and the non-daft climate model runs
Jan 22, 2016
Bishop Hill in Climate: Models

Nic Lewis has published another fascinating article about the Marvel et al paper over at Climate Audit. I was particularly taken by the discussion of the GCM runs that lay behind Marvel et al's assessment of the effect of land-use changes.

In essence, the authors did five runs of the model, with only land-use forcing changes. This tends to produce a cooling, and four of the runs gave similar results, with their average looking like this:

But one looked entirely different; like this:

I don't think they saw that coming! Apparently nobody has the faintest idea why this should have come to pass, but the authors do not think the run was "pathological". According to Nic's article, this kind of rogue run is not unprecedented either. 

Does this then mean that what hits the public realm is actually "GCM runs that don't look daft"? Either way, it doesn't leave you with a warm feeling, does it?

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